Assignment - Kinematics. Reading: Chapter 2. Objectives/HW

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1 Assignment - Kinematics Reading: Chapter 2 Objectives/HW The student will be able to: HW: 1 Define and distinguish the concepts scalar and vector. Make the connection between the visual representation of a vector and its numerical representation of magnitude and direction angle. 2 Distinguish between distance, displacement, speed and velocity Define, distinguish, and apply the concepts: position, average 6-12 speed, instantaneous speed, constant speed, average velocity, instantaneous velocity, constant velocity. 4 Define, distinguish, and apply the concepts: average acceleration and instantaneous acceleration, and constant acceleration State the displacement and velocity relations for cases of constant acceleration and use these to solve problems given appropriate initial conditions and values. 6 State and use the conditions of freefall, including the value of g, to solve associated problems Homework Questions 1. Vectors and scalars differ by one key characteristic. What is that characteristic? Create a conceptual example to show the difference. 2. If a person rode a bicycle from the Sunsphere in Knoxville, TN to Graceland in Memphis, TN, how would you state the person s position? Think in terms of relativity. 3. A weekend golfer hits a golf ball. It strikes his golf cart, a tree, a ceramic gnome, and the flag on the putting green before going into the hole. This is a very lucky shot! Describe the difference between the distance and displacement of the golf ball during this movement. 4. Physicists differ from the general population in that they view speed and velocity as different entities. If Justin Timberlake danced from the left side of the concert stage to the right side of the concert stage, then returned to his starting point in a short amount of time, how would a physicist in the audience calculate his speed and velocity? What is the difference? 5. Can acceleration be negative? Justify your answer with an example that includes text, numbers, and graphic vector representation.

2 Homework Problems (Show your work) 6. During opposition, according to Nasa, Mars and the Sun are on directly opposite sides of Earth. From our perspective on Earth, Mars rises in the east just as the sun sets in the west. If Mars is 401 x 10 6 km from Earth during opposition, what is the position of Mars relative to the Sun? Go on-line to find numbers to justify your answer. 7. You are driving down a street in a car at 55 km/h. Suddenly a child runs into the street. If it takes you 0.75 s to react and apply the brakes, how many meters will you travel before you begin to slow down? 8. A disoriented cat hunts for mice in his neighborhood. If he walks 210 meters to the north, then walks 140 meters south in a time span of 2.50 minutes, what are the speed and velocity of the cat? 9. The SR-71 Blackbird was a spy-plane. It could fly from Los Angeles to New York in 1.00 hour and 16.0 minutes. If the distance for this flight was 2451 miles, what was the average speed of the aircraft in m/s? What was the Mach speed if Mach 1 was 343 m/s? Position relative to flower (m, E) Time (s) 10. The graph above shows the motion of a hummingbird. For the interval of time shown, determine the following: (a) What is the bird s greatest distance away from the flower? (b) What is the bird s most western position? (c) At what point(s) in time is the bird at the flower? (d) Determine the bird s average velocity. (e) Determine the bird s average speed. (f) What is the bird s velocity at 10.0 s? (g) What is the bird s velocity at 5.5 s? (h) At what position(s) is the bird s velocity equal to zero? (i) What is the bird s maximum speed?

3 11. A plane flies straight north for km. Then, it turns around and heads straight back. The plane lands at an airport that is only km away from where the pilot turned around. If the plane s average velocity over the entire trip was 42 m/s, how much time did the entire trip take? 12. An athlete runs o down a straight road. Over the first meters, the runner s average velocity is 6.50 m/s. Over the remaining meters, his average velocity is 4.30 m/s. What is the runner s average velocity over the entire race? 13. Answer the following and explain or give an example: (a) Can an object have zero velocity and at the same time be accelerating? (b) Can an object have a constant speed and a changing velocity? (c) Can an object have a constant velocity and a changing speed? (d) Can an object be moving but not accelerating? (e) Can an object have velocity and acceleration vectors that point in opposite directions? 14. A woman on a bicycle accelerates from 5.1 m/s to 10.5 m/s toward the north (90.0 o ). If she does this over a time span of 4.3 seconds, what is her average acceleration? Is this reasonable? 15. After accelerating to 10.5 m/s, the same woman coasts in the same direction to a slower velocity of 2.70 m/s in 14.8 seconds. What is her average acceleration now? 16. Rocket-powered sleds were used to test the responses of humans to acceleration. Starting from rest, one sled can reach a speed of 444 m/s in 1.80 s and be brought to a stop in the next 2.15 s. The rate of acceleration due to gravity is called a "g" and is equal to 9.80 m/s 2. Determine the greatest rate of acceleration experienced by the rider and express your answer as some number of g's. 17. A soccer player scores a goal and slides across the soccer field on his knees in celebration. If she is sliding to the east at 8.6 m/s and has an average acceleration to the west at 2.41 m/s 2, how long did she take to come to rest? Is that reasonable? 18. The Velocity vs. Time graph on the next page shows the motion of an object. For the interval of time shown, determine the following: (a) At what point(s) in time is the object moving southward? (b) Find the maximum speed. (c) Find the average acceleration from t = 16 s to t = 32 s. (d) Find the acceleration at t = 4.0 s and state whether speed is increasing or decreasing at that point. (e) Find the acceleration at t = 26 s.

4 (f) The acceleration is zero at what point(s) in time? (g) The speed of the object is decreasing at what point(s) in time? 10 0 Velocity (m/s, N) Time (s) 19. An archer pulls an arrow back in a bow. The arrow is released from rest and accelerates uniformly to the east at 211 m/s 2. Determine the following: (a) What is the displacement of the arrow just before it leaves the bow at 0.67 second? (b) What is the instantaneous velocity at that point? (c) After leaving the bow, if the arrow decelerates uniformly at 0.85 m/s 2, what is the instantaneous velocity at 10 seconds into the flight? 20. A Ferrari GTB is traveling with a velocity of o. The driver applies the brakes for 2.13 seconds to come to rest. What is the displacement of the car during this motion? Is that reasonable? 21. A maglev train in Shanghai can reach km/hr. If it accelerates uniformly at a rate of 5.82 m/s 90.0 o from 312 km/hr for 8.00 seconds, at 18.0 seconds will it exceed the specified maximum velocity listed above? What is the displacement of the train at 8.00 seconds? 22. A bullet leaves the muzzle of a certain rifle with a velocity of o. The barrel of the rifle is 90.0 cm long. Find the acceleration of the bullet. 23. A driver of an El Camino going 90.0 km/h suddenly sees the lights of a barrier 40.0 m ahead. It takes the driver 0.75 s before he applies the brakes, and the deceleration rate during braking is 10.0 m/s 2. (a) Determine if the car hits the barrier. (b) Using the same assumptions, what is the maximum speed at which the car could be moving and not hit the barrier?

5 24. A bull launches a cowboy straight into the air with an initial velocity of o. (a) What is the maximum vertical displacement of the cowboy from the bull s back? (b) How long does the cowboy take to reach the maximum vertical displacement? (c) If the cowboy, somehow, lands on the bull s back, how long was he in the air? (d) What is the velocity of the cowboy, when he lands? 25. Gomer Pyle joins the Marines and learns how to fire a cannon. For some reason, he launches a shell straight into the air from the top of a 24.0 m tower with a velocity of o. (a) What is the maximum vertical displacement of the shell from the ground? (b) How long does the shell take to reach the maximum vertical displacement? (c) If the shell lands on the ground, how long was it in the air? (d) What is the velocity of the shell, when it lands?

6 Answers to selected problems 1. _ 2. _ 3. _ 4. _ 5. _ 6. _ m 8. speed = 2.3 m/s velocity = o 9. Mach a. 5.0 m b o c s & 25 s d o e m/s f o g o h. 0 < t < 4.75 s s i. 1.0 m/s 11. Accuracy check o 13. Justify your answer for full credit. a. Yes, but why? b. Yes, but why? c. No, but why? d. Yes, but why? e. Yes, but why? m/s 90 o 15. Accuracy check g s s 18. a. 0.0 s < t < 26 s b. 30 m/s c. Accuracy check d. 2.5 m/s 270 o e. 5.0 m/s 90 o f. 12 s < t < 20 s 27 s < t < 32 s 38 s < t < 50 s g. 20 s < t < 26 s 32 s < t < 38 s

7 19. a. 47 m/s 0.0 o b o c o o 21. a. Yes. By how much? b km 22. Accuracy check 23. a m b. 21 m/s 24. a o b. Accuracy check c s d o 25. a o b s c s d o

1) If the acceleration of an object is negative, the object must be slowing down. A) True B) False Answer: B Var: 1

University Physics, 13e (Young/Freedman) Chapter 2 Motion Along a Straight Line 2.1 Conceptual Questions 1) If the acceleration of an object is negative, the object must be slowing down. A) True B) False